The GATE Grind

GATE 2023 CE (CE2) – Question 30

Transportation Infrastructure · Geometric design of roadways: cross-section, sight distance, alignments · 1 mark · Multiple select

As per the Indian Roads Congress guidelines (IRC 86: 2018), extra widening depends on which of the following parameters?

  1. Horizontal curve radius
  2. Superelevation
  3. Number of lanes
  4. Longitudinal gradient

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Show answer and explanation

Correct answer: (A) Horizontal curve radius; (C) Number of lanes

Explanation

In IRC 86:2018 (and IRC 73) the extra widening on a horizontal curve is the sum of two parts.

**Mechanical widening** (the rear wheels track inside the front wheels):
$$W_m=\frac{n\,l^2}{2R}$$

**Psychological widening** (drivers keep more clearance on a curve):
$$W_{ps}=\frac{V}{9.5\sqrt R}$$

where $n$ is the number of lanes, $l$ the wheelbase, $R$ the radius of the curve and $V$ the design speed.

So the extra widening depends on the **radius** (A) and the **number of lanes** (C). Superelevation and longitudinal gradient do not appear in the formula.

Answer **A and C**.